Line pulse modulator



DCC 19, 1950 J. E. GoRHAM ET AL LINE PULSE MODULATOR Filed July 6, 1944 vom um w N MT mwJDa Patented Dec. 119, 1950 UNITED STATES OFFICE LINE PULSE MODULATOR tary of War Application `uly 6, 1944, Serial No. 543,742

(Granted under the act of March 3, 1883, ,as amended April 30, i928; 37d G. 757) 16 Claims.

The invention described herein may be manu- `iactured `and used by or for the Government for governmental purposes, without the payment to us of any royalty thereon.

This invention relates to keying circuits for radio transmitters, and more particularly to the keying circuits which periodically vkey transmitters by means of pulses of short duration.

The invention will be described by way of an example in connection with radio object locating systems, but it is obvious that the invention has a wider utility, and may be used with any type of pulse-modulated radio transmitters.

In the radio object locating systems the transmitted exploratory pulses, are, as a rule, of extremely short duration and of the highest obtainable power, the eiective operation of the systems depending to a very large extent on the power of the transmitted exploratory pulses. This type oi operation of transmitting channels requires very large concentration of power during short periods of time, and the task of delivering this power to the transmitters evolves upon the keyers, since plate modulation of the transmitters oscillators is assuming an increasingly dominant position `in operating the pulse-modulated radio systems.

The invention discloses three keyers which are capable of handling very large currents, are

stable in operation, light in wei-ght, and use com- :fi

ponents which do not differ from standard components currently used in many industrial controls of power, thus facilitating their procurement and decreasing many fold the total cost of the keyers which heretofore required specially 2.

built, expensive equipment.

In accordance with the embodiment of this invention, use is made of relatively simple pulsegenerating circuits, which are periodically discharged through a mercury pool type gaseous tube generally known in electrical power indus* try as ignitron Since ignitrons require periodic ignition, circuits are provided to accomplish this purpose, two periodically discharging artificial lines being use respectively for ign niting the ignitron and for generating the keying pulse for the transmitter. A direct current source is used for periodically charging a :drst articial line, and, upon the line being fully charged, discharging it very quickly through low impedance of a therrn-ionic tube which is rendered conductive for this `purpose by positive pulses impressed on its control grid. The irst artificial line is connected in series with the primary of a pulse transformer, the ,Secondary of.

which is connected in vser-ies with the ignitorf cathode circuit of the ignitron Thus the energy necessary for producing the ignition in the. ignitron is supplied by the energy stored in the first artificial line during its charging period. The ignitron itself acts periodically asa low yimpedance path for the second artificial line connected on one side to a high potential source, to the primary of a pulse transformer on the other side. The secondary of this pulse transformer is connected to an oscillator in the transini-ttor` The ignitron periodically shunts the series circuit formed by the second artiiicial line and the primary of the puse transformer so that the energy stored in the second line is discharged through the ignitron and through the pulse transformer, thus delivering the necessary keying pulse to the transmitter.

The advantages of such arrangement reside in the fact that very large amounts of energy may be stored in the artificial lines during relatively long charging periods, the changing rates of the two artificial lines `being so slow that they do not result in the generation of any effective pulses in the pulse transformers, and discharging the stored energies at such a rapid rate that two very powerful pulses are produced, one of which is utilized for producing the ignition in the ignitron, while the other pulse is used for keying the transmitter. Since the required power is thus obtained by storing it in the artiicial lines, large quantities of power, in the order of one megowatt or larger, may be produced with Very light equipment requiring only a small number of tubes and devoid of bulky sources of power. A single tube, an ignitron, is used for actually delivering this large power to the transmitter. An additional advantage of the invention resides in the fact that extremely accurate control of the ignition pulses, as well as ci the keying pulses, is obtainable since theV time constant of the artificial lines may be readily computed and main-tained without any further adjustments or complex apparatus for maintaining their stability. Thus the ignition and the transmitted pulses, the duration of which is in the order of only a fraction of one microsecond, are obtainable and the length of even such short may be adjusted, if there is any need, with the precision of one-hundredth of a microsecond (10AB sec).

In order to lighten the power source still further, the charging circuit of the second artic-ial line, connected to the transmitter, includes a high inductance choke con, this choke con and the articial line forming a resonance circuit so that the charging voltage impressed on the artificial line by the potential source takes the form of an oscillatory transient, the positive peak of which is equal to twice the voltage of the positive source of potential connected to the line.

According to another embodiment of the invention, two ignitrons are connected in series for discharging the artificial line connected to the transmitter, the two ignitrons acting as voltage dividers thus allowing to double the maxiinum charging voltage which divides itself oetween the two ignitrons In the last embodiment of the invention, Figure 5, the first artificial line has been eliminated and the ignition in the-ignitrons is produced directly by the pulse generating circuits.

It is, therefore, the principal object of our invention to provide a keying circuit which uses ignitrons for discharging an articial line, the line representing the component part of the keying circuit and controlling the duration of the transmitted pulses.

Another object of our invention is to provide a novel ignitor-electrode circuit for an ignitron in which the pulses impressed on the ignitor electrode are carefully timed so as to avoid rapid burning out of the ignitor electrodes even when the ignitrons are subjected to continuous operation.

An additional object of our invention is to provide a keying circuit in which an artificial line, an inductance, and an output transformer form a resonant circuit, making it possible to use a low voltage power supply.

The novel features which we believe to be characteristic of our invention are set forth with particularity in the appended claims. Our invention itself, however, both as to its organization and method of operation, together with the further objects thereof, may be best understood in connection with the following des-cription in connection with the accompanying drawing in which:

Figure l is a block diagram of a transmitted channel,

Figure 2 is a schematic diagram of a keyer using one ignitron,

Figure 3 is a schematic diagram of a keyer using two ignitrons,

Figure 4 is an oscillogram of an artificial line charging current, and

Figure 5 is a schematic diagram of a keyer using two ignitrcns the ignition of which is accomplished directly by the pulse generating circuits,

Referring to Fig. 1, an amplifier le is connected by means of a conductor l2 to a source of periodic pulses ll obtained by connecting an oscillator to overdriven amplifiers and dinerentiating networks capable of transforming the sinusoidal wave into a series of pulses of one polarity. The same result may be obtained by connecting a selfdamped oscillator to multivibrator circuits, the output of the latter being again connected to a differentiating network and pulse forming amplifiers. For a more detailed description of the pulse generating circuits, reference made to a patent application of William A. Huber and William T, Pope, Jr., Serial No. 506,808, filed October 19, 1943, titled Radio Object Locating System, and to a patent appli-cation of William A Huber titled Radio System, Serial No. 543,745, filed July 6, 1944. Normally, amplifier lil is nonconductive, this nonconductive period being utilZd for fully charging an artificial line lt whereupon pulse ll is impressed on the control grid of amplifier lll making it fully conductive, the artificial line I4 discharging to ground on one Side through amplifier l@ and through the primary of a pulse transformer l@ on the other side. The secondary of transformer l5 is connected in series with the ignitor electrode-cathode circuit of an ignitron" keyer i8. The ignitron is normally nonconductive, allowing an artificial line 29 to be charged to the highest obtainable charge. Upon reaching this maximum charge, the artificial line is discharged through the ignitron keyer i8, the latter being rendered conductive at this instant by the pulse impressed on the ignitor electrodecathode circuit by the artificial line Eli. The artificial line is so positioned in the circuit of the transmitting channel that while it discharges on one side through the ignitron keyer l, it discharges on the other side through the primary of a pulse transformer 22. The secondary of transformer 2'? is connected in series with the oscillator of a transmitter 24. it is the discharge of the artificial line E@ that finally supplies the necessary keying pulses to the oscillator of transmitter 24, the latter sending an exploratory pulse over an antenna array 2S.

Referring now to Fig, 2, where the same numerals are used for designating the same elements, amplifier lll is a three-element tube, preferably of gas-filled type, which is so biased that it is normally nonconductive. The plate of triode iii is connected to a D. C. source 2&6 over a conductor Ziiil and a choke coil 295, the latter deionizing triode lil after discharge period of artificial line lt. The amplifier is shunted to ground by artificial line I4 and the grounded primary of pulse transformer l5. When triode ID is nonconductive -condensers 299 are charged to a voltage of that portion of the potential source 286 which is connected to the anode of triode Ill; at this instant a. positive pulse ll is impressed on the control grid of triode it making it conductive, and line lil is discharged through the cathodeanode circuit of the triode on one side, and through the primary of transformer I6 on the other side. The discharge of line lll impresses the necessary ignition pulse on the ignitor electrode 298 producing the desired ionization of the igriitron` The pulses impressed on the ignitor circuit are of extremely short duration, for example, in the order of one microsecond, the duration of these pulses being timed by means of line ld which is designed to discharge during this one microsecond, The impedance through which line le discharges itself is made equal to the impedance of line lll to avoid any reflections so that the pulses impressed on electrode 208 are very sharp rectangular pulses 299. In order to avoid distortion of the pulses in the primary and secondary of transformer i6 this transformer is made according to the known practice for making pulse transformers. For a more detailed description of the behavior and the design formulae for the artificial line I4, which is sometimes called a Guillemin line, reference is made to Chapter 5 and especially to, Fosters Theorem vol. 2, Communication Networks by E. A. Guillemin, published by John Wiley and Sons, Inc., 1935. For a more detailed description of the design of pulse transformers, reference is made to an article titied Iron Core Components in Pulse Amplifiers by Reuben Lee, Electronics August, 1943, vol. 16, p. 115.

Proceeding now with the description of the ig- 5 Intron 'keycr itself, it begins with a series circuit of a. grounded source of potential 29.8., .a .chckecoil `2 Il, an artificial line :2:0 and 'the :prim ary loi pulse transformer 122.. Line '28 :is periodical-ly .charged 2416 through .coil '21M and .the primary .of transformer 22, vthis charging circuit `forming a resonant .circuit :so that the charging Avoltage :and current follow .an oscillatory transient path il lustrated .in Fig. e. The maximum voltage impressed .on line 2.0 is equal .approximately to twice the Voltage of .sourc;e.2.6., v.or .voltage 2E illustrated innig. fi, after a period .of time, which .may be 7inthe. .order of .5.0.0 microseconds, or longer. The yprix-naryoi transformer 2:2 and lineZ .fareshunted by thefcathodeenozde circuit .of ignitron 2 t2, the .ignitcon being nonconductive .during -the charging @period of line .2b. The ignition of the ignitron, as described previously, establishesan .arc between the cathode `and the ignitor electrode, and, 1oecansefo the-high positive potential :2E impressed at this instant on the anode 4or the ignitron, lthe iatter becomes :practically instantaneously fuliy ionized, thus discharging line 2U to ground through its .cathode-.anode circuit on one .side and through the primary of transformer 2:2 on the other side. The discharge of the line irnpresses the desired pulse. on the secondary of transformer 2.2 .and transmitter 2.4i which results in transmission or .an .exploratory .pulse over antenna 25. As in the `case of line 1li., :the impedance `oi the primary oi transformer and .the cathode-anode impedance of the ignitron .24.2 .are :adjusted so as te match theimpedance of .line 2li, the matching being necessary to avoid .any wave reflections which obviously `can not be f vof an arc between the mercury pool and the bracket holding :the ignition electrode .is nota constant. The arc between cathode and anode forms. almost immediately upon ignition, closing the anode circuit in a very .small fraction of .a

microsecond after the arc first bridges the meroury pool with the ignitor bracket. But .the igni- .tion time perse Avaries from cycle. to cycle, the variations following a simple statistical law. In the opera-tion under discussion, however., the rectangular -pulse .20.9 creates a potential vgraf-lient much greater than the critical ignition voltage value, and, as a consequence, the variations in time of the establishment of the arc is only in the order of a small fraction of a microsecond.

The question arises whether this veniatiolnI in the ignition time of the ignitron is of such mag nitude as. to reduire positive .synchronization hctween the triggering pulses .2539' impressed on the ignitor electron 21:08 and the charging cycle ci the Guillemin line 2), Comparison oi the time con stants involved immediately reveals the fac*l that such synchronization is in'lnecessary se of the very high inductance of coil 2M, wh: may fbe'in :the order of 19.0*290 henrys, the value of inductance 2M depending upon the desired time constant yo1V the Guillemin line with which it .forms a resonance circuit, the (L. .ation of vol-tage half-cycle T, Fig. .3, may be in the order .of v5.00.` microseconds. This .velue .of .5.09 nucrosecu .ends .compares so favorably with a Afraction of a iii,

microsecond, which vis fthe .maximum variation in the ignition time, that anysynchronization, other .than the proper timing `of the Guilleminline and of the inductance 2 Imis obviously unnecessary.

summarizing the operation of vthe keying cir cuit-illustrated in Fig. 2.,. line Mis slowly charged lby source 20.6, the charging current producing no ionization in gnitron 21.2 because of the yslow charging rate. When the line becomes lfully charged, the positive rectangular pulse ll makes triode HJ Af-.ully Conductive discharging the Guille.- vmin line I4 through the low impedances .of trode It' and :through the primary of transformer t6', the latter impressing the .ignition pulse ,on the ignitor 258. Prior to this instant, the second artificial line 2D has been fully charged by the saine `source 20"., and immediately upon rthe es tablishment of the `hot spot on the mercury pool 211i), ignitron 2:!2 flashes over and discharges line 20 :through the lpri-mary of transformer 22. This impresses the desired pulse on transmitter 21. The incluctance of the choke -coil is suiiiciently high to preclude the continuance of the ionized state in ignitron 21.2 after line `has :been dis charged. Therefore, :upon ythe discharge of line 20 ignitron 2|2 `becomes deionized and the operatingicycle of the keyer repeats itself.

The following circuit constants` and tubes give satisfactory operation of the keyer shown in Fig. 2 with a ZIE-.microsecond exploratory pulse:

D. Cfsource 206, 8,000 volts Inductance 214, 40 henrys Articial line 20:

Condensers, .04 microrara-d Coils, 6.7.5microhenrys each 'Time constant, 20 microseconds Transformer 22', 1 :to 3 step-up ratio, Hypers-il core Modulation pulse impressed on transformer 24,

1:5 megawatts Igni'rron 212, GL 4115, G. E. Co. Artificial line 14:

Condensers .093 microfarad each Coil, 11.5 microhenrys each Time constant, 1.5 microseconds Coil 205, 500 henrys Triode 1-0, 4G35 Transformer 16, 2 to 1 step-down ratio, Hypersilicore Fig. .3 discloses a .keyer which is similar in all .respects to the keyer of Fig. 2 with one rexception: two ignitrons 32.!! and .352 are connected in series vand are shunted by two resistors 3M, 3nd. The resistors connect the junction point between the choke coil 2id and line .2.8 to ground and -act .as positive means for equally dividing the max-L mum voltage impressed on the ignitrons, Two artificial lines. 32.3 and 3H), two pulse transformers .346 and SLB., and two triodes Si?. .and 3M ,are .used on the input side of the lreyer. The secD ondaries .of the transformers dit. and Si@ are connected across the cathode-ignitor circuits of the ignitrons Sill! and The functioning of this circuit is otherwise similar in all respects to the functioning of the circuit disclosed in Fig. 2. Pulses Il are impressed on the control grid of triode 312, the latterV being normally non-:zone lductive. The grid of tir-iode ills is connected to cathode resist-ance 322, this connection making tri'ode SIA to follow triode 322. Accordingly, pulse il renders the two triodes conductive simultaneously so that their artificial lines .SSS and 3M ydischarge simultaneously through triodes -3'l2 .and 314 .on lone side, and throughsthe'. primaries .of ytransformer 3|6 and 3l8 on the other side. The two ignitrons become conductive simultaneously and the articial line 30 is discharged to ground through the two ignitrons in series.

As mentioned previously two ignitrons `in series are used in Fig. 3 to double the voltage impressed on the articial line 20 in Fig, 3. Since the mercury pools in the ignitrons establish some mercury Vapor pressure within the evacuated chambers vof the lignitro-ns, they can withstand only a eertain voltage whose value is determined by the geometry of the tube and vapor pressure, any higher -voltage producing flash-over from the cathode to the anode. When the transmitters power must be increased, one of the most coni venient methods of accomplishing this result is b'y increasing the Voltage impressed on the articial line 20. ceed the flash-over value to use of a single ignitron, as illustrated in Fig. 2, becomes im- -f possible and a voltage dividing circuit, such as that shown in Fig. 3, must be used. The circuit constants for the keyer, illustrated in Fig. 3, are the same as those which were quoted for Fig. A2 except that the voltage of source 306 has been doubled. The resistors 304 and 305 are each 10 meghom resistors. It may be added here that the resistors 30!! and 365 are used to insure a more equal division at all times of the total Voltage between the two ignitrons, thus insuring the normal operation of the ignitrons and preventing accidental flash-overs.

Actual operation of the ignitrons in the keying circuits has disclosed the fact that the most sensitive element in the entire circuit is the ignitor electrode used for establishing the hot spot on the mercury pool of the ignitrons. As is well known in the art, the radio locators, as a rule, operate continuously over long periods of time, this type of operation being especially common in connection with radio locators assigned for continuous routine surveillance of the assigned areas. Since the establishment of ignition must take place in an extremely short period of time,

very large power must be delivered to the ignitor electrode, the cumulative effect of this type of operation eventually resulting in premature burning out of the ignitor electrode. It also has been discovered that the life of the ignitor electrodes, and, as a consequence, of the entire keyer, may be increased many fold if precautions are taken to prevent in some very positive manner the ignitor electrode from carrying any current immediately upon the establishment of the main cathode-anode circuit.

In the disclosed keying circuits the life of the ignitor electrode is protected by interposing the artificial line I4 in Fig. 2 and the articial lines 308 and Sli) in Fig. 3, between the triodes and the pulse transformers I6, SI5 and 318. the timing of the ignitio-n pulse impressed on the ignitor electrode does not depend on the tiniing of the rectangular pulses Il, but on the parameters of the artiiicial lines. Since the artiflcial line constants may be maintained quite cone stant, it is possible to adjust the rectangular pulses impressed on the ignitcrs so that they hardly carry any parasitic currents. This is especially true in view of the discovered fact that the variations in the ignition time or jitter `decrease very rapidly with the shortening of the ignition period; thus, with the ignition puise in the order of 1 microsecond, the jitter is reduced to a very small fraction of a microsecond,

When this voltage begins to eX- Thus,

which for practical purposes eliminates the parasitic currents.

Figure 5 discloses another modification of a line pulse modulator, the keying circuit itself being identical with the keying circuit disclosed in Fig. 3. For this reason it is not shown in Fig. 5 but the connections of ignitrons 300 and 302 may be completed by matching the dotted lines A-A in Figs. 3 and 5. The modication resides in the elimination of lines 303, 3I0 and the.y ignitor electrodes are now connected directly to a pulse transformer 500, the primary 0f which is connected to a pulse amplier 502. The remaining connections are self-explanatory. Amplifier 502 is normally nonconductive because of the negative biasing potential. Positive pulses 504 make it conductive, which in turn ionizes ignitrons 300 and 302.

The most important advantages of the disclosed line pulse modulators are the idle time periods between the keying pulses impressed on the transmitter which may be very carefully timed, and pulses of extremely short duration, from a fraction of one microsecond and up, may be generated; the modulation pulses possess very large power, such as 1.5 megawatt or higher, and the stability of the pulses from the points of View of timing and power impressed on the transmitter is very high, only minor timing variations being introduced by the jitter.

In Figures 3 and 5 only two ignitrons, connected in series for discharging the Guillemin line, are illustrated. When still higher voltages and higher modulation power are desired, it is obvious that the configuration of the circuit is such that it lends itself very readily to any desired multiplication of the number of ignitrons in the series circuit. In Figure 3 the multiplication of the number of ignitrons would require a corresponding multiplication in the number or the artiiicial lines, or, construction of a single line, which would be capable of delivering the necessary energy for producing the ignition in all ignitrons, the connections in the latter case being as those illustrated in Figure 5 with the exception that an artificial line would be interposed between triode 502 and the primary of transformer 505. In Figure 5 the multiplica-y tion of the number of ignitrons in the keying pulse generating circuit will call for no other change but the corresponding multiplication of the secondaries in the transformer 550 and of the resistances 350. Obviously enough large power will have to be delivered by triode 5%2 which may necessitate paralleling several triodes.

Ignitrons have almost unlimited peak currentcarrying capacity (several thousand amperes or more). As a consequence, a more practical method of increasing the power of the keying pulse would lie in the direction of lowering the impedance of the pulse forming line in the main power pulse circuit, and increasing the set-up ratio of the transformer connected to the transmitter. This arrangement is obviously more economical than the one calling for the multiplication of the ignitrons since it takes full advantage of the peak current-carrying capacity of the ignitrons.

Circuits are also disclosed which offer high degree of protection for the ignitor electrodes resulting in the prolonged life of this element which otherwise is the weakest point in the system. An additional advantage typical of the circuits disclosed in Figs. 2 and 3 resides in the fact that extremely low average power requirements are imposed on the pulse generating circuits,- connected to the ignitor-cathode circuit of the ignitrons, for two re'ason's first, the duration of the ignition pulses 2&9 is in the order of one micro'- second, and second, the required power is supplied b`y the artificial lines. As in the case of thev main artificial line 2E the auxiliary artificial lines I4, 308, and Slt may also form a resonant circuit with the result that the charging voltagev impressed on these lines is along the oscillatory path illustrated in Figure 4. Accordingly, large power may be'accumulated in these" ignition pulse generatingv circuits with a relatively limited power supply, the power limiting factor of the ignition pulse generating circuit being, inthe' main, the current carrying capacity of the triodes which shunt the lines' to ground. Since' the current carrying capacity of the gas-filled tubes is higher than the current carrying capacity of the vacuum tubes, the triodes lil, 3PZ, and 3M' are shown to be gas-filled triodes.

From the description ofV the line pulse modu-Y lator it is quite" apparent that the only power limiting factor in the line pulse modulators isv the Guillemin line, andv the source of potential 206 or` 306, theV remaining components of the keying circuit per se being capable of carrying very large currents. ThisA is: especially true of theA ignitrons. In the prior art the modulator tubes always constituted'the'power limiting elementA in the modulators whenever large power' requirements were imposed upon the modulators. The disclosed modulators solved this difnculty very' successfully since thecurrent carrying capacity of the ignitrons is limitedonly by the capacity of their cooling systems, the latter permit-ting currents-in the order of 5000 amperes or higher.

It is believed' that the construction andl operation of our new line pulse modulators, aswell asfthe advantages thereof, will'be apparent from foregoing description. It will, therefore, beapparentthatr while wehave shown and described our invention in' several' preferred forms, many changes and modifications may be made without departing from the spirit of our invention as soughtto be denned in the following claims.

We claim:

1. A keyer for a radio transmitter including a series circuit of'a source of potential, an impedance, an artificial line, and means interconnecting' said artificial line to said transmitter, said series circuit comprising a resonantnetwork, and aA gas-discharge tube pathshunting said arti- 'cial line and said means,.saidtub"e`path periodically discharging said articialiline' for generate ing keying pulses through saidmeans for said transmitter.

2:y In ar keying circuit for a transmitter', a series resonant circuit including a source of p"o`-' tential; a choke coil, an articial lin'e, and a, cou-- pling lmeans, said coupling means electrically coupling said series circuit to said transmitter, and said source of potential periodically charging said line, a gas-discharge tube path shunting saidarticial line and'said'co'u'p'ling mea-ns, and azsource'of pulses rendering-saidftube pathlconductive in synchronism with the appearance of the maximum charge on said artificial line.

3. In a keying circuit for a transmitter, a coupling means between said keyer and said transmitter, a serially connected artificial line and a choke coil, said choke coil being connected to a source of potential, and said line being connected to said coupling means, said source of potential 1G periodicallyv charging said artificial line, a gasdischarge tube having a cathode, an anode, and an igniter electrode, the' cathode-anode circuit of said tube serving to shunt said artificial line and sai'd coupling means, and a source of pulses;

renderinglsai'd tube conductive in synchronism with the appearance of the maximum charge on said artificial line', said artici'al line, choke coil,I

shunt said artificial line and said means, andk a source of pulses connected across said cathode and said igniter electrode' for producing ionization in saidtriode whereby said articial line discharges through said triode and through said means, the discharges of said line generating modulation pulses forsaid-transmitter.

5. Aline pulse modulator connected to atransinitter, said modulator including a seriesv circuit of a source of potential grounded with its negative terminal, a choke coil, an artificial line and a primary of a" step-up transformer', the secondary ofv said transformer being connected to said transmitter, said series circuitv forming a` series resonant network, and the ihputimpedance ofv said transformer substantially matching the characteristic impedance of said artificial line, a gas-discharge tube connected between ground and the junction point between said choke coil and said artificial line, and-a source of periodic pulses connectedv to saidv tube, said pulses and said artificial line rendering said tube periodically conductive'- whereby said line discharges l through said tube and through the primary of said transformer, the discharges of said line through said transformer producing keying pulses for said transmitter.

6: A keyer for a radio transmitter as dened in l claim 5 in which said gas-discharge tube comprises a'triode including a, mercury pool cathode,

anigniter electrode, and an anode, said sourceV of pulses being connected across the igniter electrode-cathode circuit of said triode.

'7. A keyer for a radio transmitter asdeiined in` ignitor electrode', andv an' anode,V and said source of pulses'further comprises a source of periodic signals, a second gas-discharge tube which also comprises a triode including a cathode, a control' g-ridand an anode connected witliits'grid to I said source of signals, said signals periodically rendering said second triode conductive, a second articial line connected with one end to the anode of said second triode, and a coupling means connected to the other end of said second line, said means connecting said second artificial line to the ignitor electrode-cathode circuit of the first gaseous triode.

articial line, a source of periodic pulses con-Y nected to said control grid rendering said tube periodically conductive for discharging said arti- Y ficial line through said tube and through said transformer, a second series circuit including a source of potential, a second choke coil, a second artificial line, and a primary of the second transformer, a second gas-discharge tube shunting Said second articial line and the primary of said second transformer, said second tube having a pool of ionizable reconstructive cathode material, an anode, and an ignitor for said cathode, the cathode-ignitor circuit of said second tube being connected across the secondary of said first transformer, anda transmitter connected to the secondary of said second transformer, said rst and second series circuits and said tubes being so constructed and arranged that said iirst series circuit periodically produces an active cathode area in said second tube, and said second series circuit periodically produces modulating pulses for said transmitter.

10. A line pulse modulator including a series resonant circuit comprising a source oi potential, an impedance a network capable of storing electrical energy, and coupling means connecting said network to a transmitter, an ignitron having an 5 ionizable reconstructive cathode, an ignitor electrode, and an anode, the cathode-anode circuit of said ignitron shunting said network and said coupling means, and a source of periodic pulses microseconds connected across'the cathode-ignitor circuit of said ignitron, said pulses establishing an active area on said cathode for shorting said network through said ignitron and of establishing substantially simultaneously active cathode areas in said ignitrons.

14. A keyer for a radio transmitter as defined in claim 11 which further includes a source of periodic pulses, a vacuum tube amplier con- 'having a duration in the order of from 0.5 to 10 .n

through said coupling means for generating modulation signals for said transmitter.

11. A keyer for a radio transmitter including a series resonant circuit of a source of potential, an impedance, an articial line and a coupling means, said coupling means connecting one end of said artificial line to said transmitter, and two l serially connected ignitrons shunting said articial line and said coupling means, said ignitrons perodically dischargng said articial line through their cathode-anode circuits and throughv said coupling means for generating keying pulses for said transmitter.

12. A keyer for a radio transmitter as deiined in claim 11 which further includes two serially connected resistances, one of said resistances shunting the cathode-anode circuit of one ignitron and the other resistance shunting the cathode-anode circuit of the other ignitron.

13. A keyer for a radio transmitter as defined in claim 11 which further includes a source of periodic pulses connected to the ignitor-cathode circuit of each ignitron, said source being capable nected to said source, and a transformer having one primary and two secondaries, said primary being connected to said ampliiier, and said'secondaries being connected across the ignitor electrode-cathode circuits of said ignitrons respectively.

15. A keyer for a radio transmitter as defined in claim 11 which further includes a source of periodic pulses, a second coupling means, a second artificial line connected between said source of potential and said second coupling means, said second coupling means being also connected to the ignitor electrode-cathode circuits of said ignitrons, and a gaseous discharge path shunting said second artificial line and said second coupling means for periodically discharging said second artiiicial line through said gaseous discharge path and said second coupling means, the discharge of said second articial line generating 3 the ignition pulses for said ignitrons.

16. A keyer for a radio transmitter as defined in claim 11 which further includes a second series circuit of: said source of potential, an impedance, Va second artiiicial line and a second coul, pling means; said second series circuit having parameters making said second circuit a seriesresonant circuit, said second coupling means being connected across the ignitor, electrode-cathode circuits of said ignitrons, a gaseous triode shunting said second artificial line and said second coupling means for periodically discharging said second articial line through said gaseous triode and through said second coupling means, and a source of pulses rendering said gaseous triode conductive in synchronism with the appearance of the maximum charge on said second artificial line.

JOHN E. GORHAM.

WALTER T. SILVER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,266,401 Reeves Dec. 16, 1941 2,288,544 Smith, Jr June 30, 1942 2,391,894 Gorham et al Jan. 1, 1946 2,400,457 Haine May 14, 1946 2,405,070 Tonks et al July 30, 1946 2,411,898 Schelleng Dec. 3, 1946 2,416,718 Shockley June 10, 1947 2,420,309 Goodall May 13, 1947 g 2,422,086 Evans June 10, 1947 2,432,227 Dailey et al Dec. 9, 1947 2,462,918 Stiefel Mar. 1, 1949 FOREIGN PATENTS 5 Number Country Date 489,021 Great Britain Oct. 15, 1936 245,582 Italy Mar. 2, 1926 

